Stability and Dewetting of Metal Nanoparticle Filled Thin Polymer Films: Control of Instability Length Scale and Dynamics

Abstract

We investigate the influence of gold nanoparticle addition on the stability, dewetting, and pattern formation in ultrathin polymer-nanoparticle (NP) composite films by examining the length and time scales of instability, morphology, and dynamics of dewetting. For these 10-50 nm thick (h) polystyrene (PS) thin films containing uncapped gold nanoparticles (diameter approximately 3-4 nm), transitions from complete dewetting to arrested dewetting to absolute stability were observed depending on the concentration of the particles. Experiments show the existence of three distinct stability regimes: regime 1, complete dewetting leading to droplet formation for nanoparticle concentration of 2% (w/w) or below; regime 2, partial dewetting leading to formation of arrested holes for NP concentrations in the range of 3-6%; and regime 3, complete inhibition of dewetting for NP concentrations of 7% and above. Major results are (a) length scale of instability, where lambdaH approximately hn remains unchanged with NP concentration in regime 1 (n approximately 2) but increases in regime 2 with a change in the scaling relation (n approximately 3-3.5); (b) dynamics of instability and dewetting becomes progressively sluggish with an increase in the NP concentration; (c) there are distinct regimes of dewetting velocity at low NP concentrations; (d) force modulation AFM, as well as micro-Raman analysis, shows phase separation and aggregation of the gold nanoparticles within each dewetted polymer droplet leading to the formation of a metal core-polymer shell morphology. The polymer shell could be removed by washing in a selective solvent, thus exposing an array of bare gold nanoparticle aggregates.

Microscopic dynamics in nanocomposite photosensitive films studied by X-ray photon correlation spectroscopy

“…These results are very similar to what we recently measured in a XPCS experiment on multilayers of pure PA4 [9], suggesting that the dynamics of nanoparticles can be used to investigate the internal dynamics of the polymer, in analogy with previous measurements on glassy polymer melts [3]. This is particularly true given that the GNP concentration is low enough to leave the mechanical properties of the polymer unaffected [20][21][22].…”

“…Even if we used two different concentrations, both of them are sufficiently low to not alter the mechanical properties of the GNP/polymer composite which are the same as in the pure polymer at these low concentrations [20][21][22], thus leaving only temperature and illumination as parameters governing mechanical properties. On the contrary, for higher GNP concentrations, in the regime of a few percent and above, mechanical properties of GNP/polymer composites are known to be altered in a progressive way as the concentration is increased [20][21][22]. This is known in general for many GNP/polymer combinations, furthermore we characterized the interfacial shear modulus G* for our particular case of GNP/PA4 for different concentrations up to 5%, finding that G* is not affected by the presence of GNP for concentrations below 0.5% in weight [23].…”

The stability of thin polymer films as controlled by changes in uniformly sputtered gold

“…16 -18 Thin PS films (> 20 nm thick) on native SiOx covered Si wafers are metastable and can dewet via nucleation. 16,18 The potential Φ(h) for such uncovered PS thin films described by Provided the potential barrier can be breached, either by thermal 5 fluctuation or the presence of defects, a lower film thickness can be reached, and so the film is conditionally unstable. In contrast, PS films on thicker SiOx 16 can always reduce their energy by simply lowering their thickness (curve 2, Figure 1); they are therefore unstable and dewet spinodally.…”

“…Combining thin polymer films with nanoparticles (NPs), [1][2][3][4][5] or 20 thin continuous layers [6][7][8] of metallic or dielectric materials, can lead to new materials with unique electrical, mechanical, optical or antimicrobial properties for use in devices and coatings. Metallized thin polymer films have many applications ranging from decorations to diffusion barriers in food packaging to 25 dielectric layers in microelectronics.…”

“…11,12 These nanometer sized objects are referred to in the present study as nanoparticles. 4,[11][12][13] The particle aggregation process during their diffusion on thin polymer films is relatively well understood, 12 but their influence on the stability of polymer films 1,4,5 is still at 35 an early stage. Thin polymer films on solid substrates become unstable at temperatures larger than the glass transition temperature (Tg) and dewet.…”